The primary goal of this application is to determine the mechanism by which changes in the formulation of the alloy reduce mercury (Hg) release from dental amalgam. A series of alloys will be prepared to test specific hypotheses about the effect of palladium (Pd) additions, silver (Ag) and tin (Sn) ratio, and copper (Cu) content. The composition of the pre-trituration alloys and the resulting amalgams will be evaluated by scanning electron microprobe and scanning transmission electron microscopy with micro-diffraction and XEDA to correlate changes in Hg release with microstructure. In addition, amalgams will be prepared from alloys mixed with pure Hg and indium (In)-Hg alloys to further understand the effect of indium on reducing Hg release, and to produce minimal Hg-releasing formulations. The investigators expect to identify commercially viable amalgams with reduced Hg vaporization during setting and after abrasion, and reduced Hg dissolution. The physical properties of these amalgams will be evaluated to verify that they are adequate for clinical use and to further describe the effect of composition on properties. Dynamic dissolution into both neutral saline and acidic solutions, as well as thermal properties, will be assessed to correlate the stability of the amalgams with composition. Finally, Hg release from aged amalgams will be correlated with changes in their microstructure. The primary hypothesis is that Hg release will be minimized when the Ag-Hg matrix phase of amalgam is most effectively stabilized and its surface oxidized and that this is accomplished by maximizing the amount of Sn present in the gamma one matrix. There are four aims: to identify the mechanism by which additions of Pd, changes in the Cu content, and alterations in the Ag and Sn concentrations in dental amalgam alloy affect the vaporization of Hg; to identify the mechanism by which those variables affect the dissolution of Hg from dental amalgam; to verify that the new alloys produce amalgams with acceptable physical properties; and to verify that the amalgams are stable over a two year period.